1. Technical Field
The present invention relates to a magneto rotor used in generation of ignition timing pulses, provided in a magneto of an internal combustion engine ignition device etc.
2. Related Art
A magneto rotor of the related art is shown, for example, in FIG. 3 and FIG. 4. The rotor has a balance weight section 20 and a pair of magnetic poles 30 and 40 integrally formed with a rotor core 10 for rotating in the vicinity of a generating coil, not shown. The pair of magnetic cores 30, 40 are provided on a side opposite the balance weight section 20 with respect to a center of rotation O of the rotor core 10.
A magnetic steel magnet 50 is fitted between the magnetic poles 30 and 40 such that both sides are inserted into slots 30a and 40a formed in opposite surfaces of the magnetic poles 30 and 40. A magnetic gap G for exerting a magnetic field focused on the generating coils is then provided at an outer side of the magnet 50, between the magnetic cores 30 and 40.
Also, the rotor core 10 is molded together with the magnet 50 inside a rotating disk 60 formed of a nonmagnetic member such as synthetic resin, for example, and tips of the magnetic poles 30 and 40 protrude outward slightly from the peripheral surface of the rotating disc 60. Reference numeral 70 is a shaft hole into which a crankshaft of the internal combustion engine is inserted.
In the magneto rotor, magnetic flux generated by the magnet 50 is generated as a sharp pattern magnetic field from the magnetic gap G between tips of the magnetic cores 30 and 40. This magnetic field repeatedly passes through the vicinity of the generating coil with rotation of the rotor core 10. Because of this, a voltage corresponding to the strength of the magnetic field is induced in the generating coil, and it is possible to cause discharge of ignition current from the condenser charged with this voltage into the ignition coil at a fixed timing. As a result, the internal combustion engine is started and driven.
However, with the rotor of the related art, the magnet 70 is subjected to centrifugal force at the time of high speed rotation of the rotor core 10 and generates force so as to fly outwards, this force acts to force open the magnetic gap G and finally there is a danger of deformation and damage to the magnetic poles 30 and 40 themselves and damage to the rotating disc 60.
On the other hand, in order to prevent the magnet 50 flying outwards in this way, a method of binding the magnetic poles 30 and 40 holding the magnet 50 with a band has been considered, but since it is necessary to connect the ends of the band each other with a separate piece, as well as there being a large cost increase there is a problem that the external dimensions of the connecting section of the band ends are increased posing an obstacle to miniaturization of the rotor.